function A() {
  return new Promise((resolve) => {
    setTimeout(() => {
      console.log('异步A');
      resolve()
    }, 1000)
  })
}
function B() {
  return new Promise((resolve) => {
    setTimeout(() => {
      console.log('异步B');
      resolve()
    }, 500)
  })
}
function C() {
  return new Promise((resolve) => {
    setTimeout(() => {
      console.log('异步C');
      resolve()
    }, 100)
  })
}

